1. Field of the Invention
This invention relates to rotator drive devices, and more particularly to a phase control device for a rotator.
2. Description of the Prior Art
In the conventional rotator drive device, for example, the disk drive device in the electronic still camera, it has been the common practice that the driving of the disk in such a manner to control phase of rotation of the electric motor is brought into coincidence with the clock signal which is used for regulating the timing in operating the camera whole. The use of such a method in controlling the speed (phase) of the motor, therefore, took a very long time. Thus, in the various operations of the camera, its ramp characteristic was less than desirable.
Also, a method of phase control may be considered in which the phase of an FG (Frequency Generator) pulse is synchronized in a delay of .pi. from the clock signal. In this case, however, the possibility of controlling the phase is unavoidably limited so that the phase lag of the FG pulses with respect to the clock signal must fall in a range from 0 to not more than 2.pi..
Yet, with a sudden change of the load on the motor, the phase difference may likely exceed the above-defined maximum acceptable range.
For example, suppose, for every one revolution of the rotator (not shown), 16 FG pulses are obtained. If in this case, as the phase difference between the clock signal and the FG pulse was in the close neighborhood of (15/8).pi. at the time of the (n-1)th cycle of sampling for control, the phase of the FG pulse delays more than (1/8).pi. from the clock signal until the next or nth cycle of sampling. As a result, a phase lag of the FG pulse to the clock signal above 2.pi. occurs. In the above-described control method, this situation is mistaken for a diminishment of the phase gap, because phase lags of 2.pi. and zero cannot be discriminated from each other. Therefore, proper control could no longer be attained.
Hence, there has been demand for a rotator drive device having phase control capable of following larger variations and sudden changes in the load.